The present invention relates generally to a method for use as a liquid impregnator or as a washer or rinser in the continuous wet processing treatment of fibrous assemblies, and especially for use in processing continuous nonwoven batts or webs. Such continuous textile treating processes are frequently referred to as continuous "pad-dry" processes. Generally such continuous pad-dry processes begin with a "wet-on-dry" application stage in which the fiber assembly (batt, web, or fabric), hereinafter referred to as a batt, is fed as a continuous dry fiber batt into the first liquid impregnating stage. Following this first wet-on-dry impregnation, the web batt generally passes through the nip of a pair of high expression nip rolls to reduce the liquid (i.e., the treating "liquor") pickup to some level below that present on the batt before entering the nip of the high expression paired nip rolls. The wet pickup (WPU) of liquor on the batt as it leaves the impregnation tank and before passing through the high expression paired nip rolls may be on the order of 1,000% to 4,000% (meaning 10 to 40 pounds of liquor per pound of dry fiber in the batt) depending upon the porosity, capillarity and wet bulk of the batt, the time and distance required for the batt to emerge from the impregnating bath to the high expression paired nip rolls, and the nature of the impregnating liquor.
The design of the high expression paired nip rolls and the pressure applied to the batt at the nip of the high expression paired nip rolls may be varied to obtain various levels of residual wet pickup of liquor on the batt as it leaves the paired nip rolls. The desired level of residual wet pickup depends upon the nature and purpose of the next process stage. Generally, if the next process stage is a second wet impregnation stage (and hence a "wet-on-wet" impregnation stage), it is desirable to reduce the level of residual wet pickup on the fabric by means of the high expression paired nip rolls to as low a level as practicable in order either (a) to provide for sufficient additional wet liquor pickup on the batt during the subsequent wet-on-wet impregnation, or (b) to minimize the residual wet pickup on the batt before the batt enters the dryer. If the process stage following the paired nip roll expression is a "reacting" or "aging" stage, the desired level of wet pickup on the batt leaving the high expression paired nip rolls may be higher than the minimum level which can be achieved by very high pressure expression nip rolls.
Somewhat higher residual wet pickups may be desired to provide sufficient liquid mobility throughout the large and small capillary spaces between fibers in the fibrous assembly which forms the batt. Such liquid mobility is desirable during a "reacting" or "aging" period in the process to assure good distribution of chemical reactants such as alkali, hydrogen peroxide bleaches, dyestuffs, etc., throughout the batt. Frequently, high expression of liquor at the nip of the high expression paired nip rolls just prior to the rinsing stage or between each of a series of rinsing stages is also sought in order to reduce the amount of rinsing liquid used and to improve the rinsing efficiency of each rinsing stage.
It is readily apparent that, in continuous wet chemical textile finishing or treating processes, the design and resulting efficiencies of the various liquor impregnation stages and liquor extraction stages (high expression paired nip rolls are used in this illustrative discussion to serve as the liquor extraction means) play a major role in the cost of such process equipment and the effectiveness of such process methods. In order to achieve thorough impregnation of treating liquors into textile fabrics, or thorough rinsing of residual chemicals from such treated fabrics, two or more tandem "dip and nip" impregnators or wash boxes are frequently used. And for woven fabrics, the dwell time and washing or rinsing efficiency is generally improved by increasing the path length through which the fabric must travel in the washing or rinsing liquor. To obtain sufficient path length in such wash boxes, woven fabrics travel over and under a large number of rolls spaced relatively far apart (roughly 3 to 12 feet) vertically, and relatively close together (roughly 0.5 to 1.0 foot) horizontally. In this manner, a fabric passing over, say, 31 rolls and under 30 rolls (alternately over and under one roll to the next) will travel 120 yards in a wash box measuring roughly 16 feet long.times.7 feet high if the rolls are spaced 6 inches apart horizontally and 6 feet apart vertically.
At high linear speeds of woven fabric traveling through the wash box plus counter current flow of wash liquor relative to the fabric travel through the wash box, good exchange of fresh rinse liquor for residual treating liquor in the fabric can be achieved. Many innovations in design of washers have been made to increase liquor penetration and exchange for both wet-on-wet impregnators and for wash boxes, with many of these designs employing means to generate turbulent liquor flow, forced flow of the liquor through the fabric as it passes over suction drums or slots, etc.
In seeking to improve the design of impregnators and wash or rinse boxes for nonwoven fiber assemblies, for example a 16 oz. per square yard carded or garnetted cotton batt, it is not practicable to attempt to pass the batt up and down long vertical distances over a series of rolls as described above for a woven fabric, since the nonwoven fabric or batt does not have enough strength to hold together as it travels long spans up and down over such a series of rolls so spaced. One alternative is to pass the nonwoven batt under a shallow immersion roll and then through the nip of a pair of squeeze rolls. However, to achieve an efficient, thorough wet-on-wet liquor exchange or rinsing effect it is necessary to pass the batt through a number of such "dip-and-nip" stages in tandem sequence with one another. By using a shallow (essentially horizontal) immersion path through each dip tank the fiber batt can be transported on one conveyor belt (rather than between two belts) with little or no risk of breaking the batt as it passes into, through, and out of the dip tank and then to the nip of the paired squeeze rolls. Unfortunately, however, the equipment cost for a multi-stage series of single-dip-single-nip wash boxes or impregnators becomes economically burdensome. A major cost factor is each pair of squeeze rolls needed for each high expression nip following each impregnation dip. During immersion, it is also important that the web be treated without a substantial stretching of the web. One way of avoiding excessive stretching of the web is to convey the web through a treatment tank in a generally longitudinal direction with relatively short up and down fluctuations in the path of the web.
Various designs for impregnators or rinsers which have been disclosed prior to the present invention are unsatisfactory since they employ either one or two conveyor belts to pass between the nip of paired high expression rolls or between stationary paired pressure plates, or they require the batt itself to pass between the nips of a series of high expression paired nip rolls to achieve satisfactory liquor exchange or rinsing efficiencies. For example, to increase the effectiveness of the action of the fluid on the web, a repetitive squeezing of the web during travel within the tank has been utilized by providing a sequence of paired squeeze rollers or stationary pairs of opposed pressure plates along the path of the web such as is shown in U.S. Pat. No. 3,681,951 issued to Chaikin et al. Other fluid treatment systems include a sequence of rollers arranged in a generally circular configuration to provide a sort of zigzag path for the web. A single conveyor belt has been used with such a roller arrangement such as is shown in the German Patent No. 1,460,397 issued to Freudenberg on May 29, 1969. In this arrangement, however, a central roller cooperates with the circular arrangement of rollers to provide a repeated paired nip roll squeezing action of the web between the central roller and adjacent rollers. The Freudenberg arrangement is also undesirable because it is unsuitable for use with a countercurrent flow.
Other attempts at providing a fluid treatment system having a series of rollers and one or more conveyor belts are described in U.S. Pat. No. 3,457,740 issued to Korsch, and U.S. Pat. No. 2,742,773 issued to Chambers et al.
However, the need still exists for an efficient, economical apparatus and method for impregnating and/or washing a nonwoven batt, particularly adapted for use in a continuous fashion.
It is an object of the present invention to provide a method which substantially avoids or alleviates the problems of the prior art.
It is an object of the present invention to provide a method for fluid treatment of a web of fibers by intermittently gently squeezing the web within a tank of fluid.
Another object of the present invention is to provide a method for fluid treatment of a web of fibers by conveying the web on a single endless belt alternately beneath a squeeze roller and above a cooperating roller.
Yet another object of the present invention is to provide a fluid treatment for a web wherein the web is conveyed on a single endless conveyor belt and travels in a generally horizontal direction so as not to be excessively stretched during the fluid treatment.
Still another object of the present invention is to provide a method for a fluid treatment of a batt in which the batt is repeatedly compressed and allowed to expand between compressions during the treatment within a tank of fluid.
An apparatus which satisfies these and other objects includes a longitudinal tank and a perforate endless conveyor belt which carries a non-woven web of fibers into the tank and beneath a first squeeze roller. The perforate conveyor belt may travel entirely within the longitudinal tank or alternatively the belt may pass underneath the tank while the belt is not carrying the non-woven batt. The web is generally squeezed in a nip defined between the conveyor belt and the squeeze roller to remove fluid from the web. The conveyor then carries the web over a first singular or cooperating roller and to the next squeeze roller. The web, after being gently squeezed, expands significantly to absorb fluid in the longitudinal tank as the web passes from one squeeze roller, over the intermediate cooperating roller and to the next squeeze roller. The conveyor belt repeatedly carries the web alternately beneath a squeeze roller and above a cooperating roller throughout the longitudinal tank to repeatedly squeeze the web. Fresh fluid may be supplied to the tank by way of one or more orifices positioned above the tank or alternatively fluid may be supplied from a collecting tank which is located beneath the longitudinal tank. The fluid generally travels in a direction opposed to the direction of travel of the web to continuously provide relatively fresh fluid for the web throughout the longitudinal tank.